Communications systems and datacenters are required to handle massive amount of data at ever increasing speeds and ever decreasing costs. To meet these demands, optical fibers and optical ICs (such as, a photonic integrated circuit (PIC) or an integrated optical circuit) are used together with high speed electronic ICs. A PIC is a device that integrates multiple photonic functions (similar to an electronic IC or radio frequency (RF) IC). PICs are typically fabricated using indium phosphide or silicon oxide (SiO2), which allows for the integration of various optically active and passive functions on the same circuit.
The coupling of PICs to optical fibers is not as well advanced as the integration and/or coupling of electronic ICs. Specifically, the challenges facing optical connections are different and much more complex than connecting electronic ICs to, for example, a printed circuit board (PCB). Some difficulties are inherent in wavelength, signal losses, assembly tolerance, and polarization characteristics of optical packaging.
Existing solutions utilize various techniques for connecting optical fibers to PICs. One technique suggests using various types of butt connections to the edge and surface fiber connections a PIC. The butt of a fiber can be connected to a planar waveguide at the edge of a PIC. This technique is efficient only if the cross section of the propagating mode of the fiber and the waveguide areas of the fiber core and the waveguide are of similar size. In most cases, this technique suffers from poor assembly tolerance.
Another technique suggests laying a section of fiber on top of the surface of the PIC where the end of the fiber has been cut at an angle to form an angled tip. The angled tip has a flat surface which reflects a light beam down to a waveguide grating coupler disposed on the integrated circuit. The light beam is reflected off the reflective surface of the angled tip by total internal reflection. The waveguide grating coupler is designed to accept the slightly diverging light beam from the reflective surface of the angled tip of the fiber. The light beam can also propagate through the fiber to a chip coupler in the opposite direction, up from the substrate, through the waveguide grating and into an optical fiber after bouncing off the reflective surface of the angled tip. This technique further requires coating the exterior of the reflective surface with an Epoxy.
Among others, all of the above-noted techniques require precise alignment, and thus active positioning of the optical fiber to the PIC. As such, current techniques suffer from poor and very tight alignment tolerance to gain an efficient connectivity. For example, a misalignment between an optical fiber and a PIC of 1-2 microns (μm) would result in a signal loss of about −3 db. Furthermore, the alignment is now performed with expensive equipment or labor-intensive assembly solutions. As a result, mass production of PICs and/or optical couplers is not feasible.
The lack of a reliable and efficient solution for optical coupling of PICs also limits the ability of mass production for an electrical-optical interconnection platform that allows multiple-chip connections via electrical and optical connections.
As an example, one typical arrangement of electrical-optical interconnection platform is based on a silicon photonic interposer. Such an interposer may be utilized in a hybrid integration of photonics and electronics by face-to-face bonding (flip-chip assembly). In such arrangement the I/O fibers are connected to waveguides pre-designed in the silicon interposer. The silicon photonic interposer includes vias created through the silicon to provide the electrical path to/from the PCB substrate and the optoelectronic devices inside the silicon photonics die. The optical transmission is inside the silicon photonics die.
Another arrangement discussed in the related art, is a multi-substrate electro-optical structure. The structure includes a substrate mounted over a supporting PCB. The substrate interconnections between optical chips, mounted on the silicon photonic interposer, and IC chips.
The typical arrangements discussed above are based on a silicon photonic interposer. Such an interposer typically includes active and passive optical devices (e.g., photo-detectors, modulators, splitters, etc.). An “active” interposer is an expensive component manufactured using a complex process. Further, the optical source (e.g., laser light) is coupled to the silicon photonic interposer via an optical fiber and grating coupler, or via an edge-coupling or any other equivalent optical coupling. As noted above, such coupling techniques require precise alignment and active positioning of the optical source to the PIC or the interposer.
Another solution for electrical-optical interconnection platform includes assembling of discrete electrical and optical device on a silicon photonics substrate. The electrical connection is achieved using electrical pins formed using through glass vias (TGV) while optical connections are formed using optical pins. The optical pins are structured using optical grating couplers. As noted above, such couplers do not demonstrate good tolerance for misalignment. As a result, a mass production of PICs and/or optical couplers of the various electrical-optical interconnection platform solutions discussed in the related art may not be feasible.
It would therefore be advantageous to provide an efficient electrical-optical interconnection platform that would overcome the deficiencies of the existing solutions.